The balanced chemical equation for the reaction between hydrogen and oxygen to form water is:

2H2 + O2 → 2H2O

According to the equation, 2 moles of hydrogen react with 1 mole of oxygen to form 2 moles of water. The molar mass of hydrogen, oxygen, and water are 2 g/mol, 32 g/mol, and 18 g/mol respectively.

Using the given masses of hydrogen and oxygen, we can calculate the number of moles of each element present:

Number of moles of hydrogen = 80 g / 2 g/mol = 40 mol
Number of moles of oxygen = 80 g / 32 g/mol = 2.5 mol

Since oxygen is the limiting reagent, only 2 moles of water can be formed. Therefore, the mass of water formed can be calculated as:

Mass of water formed = 2 mol x 18 g/mol = 36 g

Therefore, 36 g of water is formed in this reaction.


The limiting reagent is the reactant that is completely consumed in a reaction, limiting the amount of product that can be formed. In this reaction, oxygen is the limiting reagent because it is present in a smaller amount than required for the reaction to proceed fully.


The excess reagent is the reactant that is not completely consumed in a reaction, remaining after the limiting reagent is completely consumed. In this reaction, hydrogen is the excess reagent because it is present in a larger amount than required for the reaction to proceed fully.

The mass of excess hydrogen can be calculated as follows:

Number of moles of hydrogen required for reaction = 2.5 mol x (2 mol H2 / 1 mol O2) = 5 mol H2
Number of moles of excess hydrogen = 40 mol – 5 mol = 35 mol

Therefore, the mass of excess hydrogen can be calculated as:

Mass of excess hydrogen = 35 mol x 2 g/mol = 70 g

Therefore, 70 g of hydrogen is in excess in this reaction.

limiting reagent is O2. 5 miles of water is formed i.e 90g of water.70 g of h2 is extra.